Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and Media Access Control (MAC) specifications for implementing Wireless Local Area Network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
WLAN devices are currently being deployed in diverse environments. These environments are characterized by the existence of many Access Points (APs) and non-AP stations (STAs) in geographically limited areas. Increased interference from neighboring devices gives rise to performance degradation. Additionally, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. Video traffic, in particular, is expected to be the dominant type of traffic in WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance.
In a task group called Institute of Electrical and Electronics Engineers (IEEE) 802.11ax, High Efficiency WLAN (HEW) standardization is under discussion. The HEW aims at improving performance felt by users demanding high-capacity and high-rate services. The HEW may support uplink (UL) and downlink (DL) multi-user (MU) simultaneous transmissions, which includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) transmissions.
In IEEE 802.11 systems, the MAC header of a MAC Protocol Data Unit (MPDU) may include a High Throughput (HT) Control field that is used to carry control information. The HT Control field may have a different field format depending on the variant. Some possible variants include the HT variant (for IEEE 802.11n) and the VHT variant (e.g., for IEEE 802.11ac). The HT Control field is typically four bytes in length. IEEE 802.11ax introduces a new field called High Efficiency Aggregated Control (HE A-Control) field that may replace the HT Control field. The HE A-Control field includes one or more High Efficiency (HE) Control subfields, where each HE Control subfield is used to carry a particular type of control information.
IEEE 802.11ax systems may allow the control information carried in the HE A-Control field to be different from one MPDU to another MPDU within the same Aggregated MPDU (A-MPDU). Also, some control information may be allowed to be repeated within the same A-MPDU. With these possibilities, there is a need to define the structure and rules of the control information that can be carried in the HE A-Control field to allow for unambiguous operation.